Electron tube amplifier



- J n. 25, 1955 J. B. MlNTER, 2ND

ELECTRON TUBE AMPLIFIER Filed Jan. 13; 1949 TIME * TIME TIME m 2 H mm m El 0 M M n 4 40% aw m m .l. keb a a aw 5 J 0 w M1 w b r I a x United States Patent ELECTRON TUBE AMPLIFIER Jerry B. Minter 2nd, Boonton, N. 1., assignor to Measurements Corporation, Boonton, N. J., a corporation of New Jersey Application January 13, 1949, Serial No. 70,779

10 Claims. (Cl. 179-171) This invention relates to electron tube amplifiers or repeaters and more especially to amplifiers capable of efiiciently and faithfully amplifying or repeating waves having steep rising or falling wave fronts.

A principal object is to provide an improved electron tube amplifier which has the advantages of the wellknown cathode follower type of amplifier, but without certain disadvantages of that type of amplifier.

Another object is to provide an electron tube amplifier which is eminently well-suited to amplify with precision, positive and negative pulses.

Another object is to provide an electron tube amplifier of the type having a cathode load output circuit, and wherein the output impedance of the amplifier is maintained at a low value both for negative as well as positive input signals.

A feature of the invention relates to an electron tube amplifier of the generic cathode load output type, and wherein the magnitude of the cathode load impedance is controlled by both positive and negative input pulses.

Another feature relates to an electron tube amplifier having a grid-controlled tube whose cathode return includes a load resistor which is connected to an output circuit including an integrating device such as a capacitance, in conjunction with another grid-controlled tube which forms said load resistor and whose plate resistance is varied in opposite phase with respect to the phase of the input signals.

A further feature relates to an electron tube amplifier having a first grid-controlled tube with a cathode follower load in the form of another grid-controlled tube, and with the cathode of the first tube connected to an output circuit containing substantial capacitance, in con junction with another grid-controlled electron path connected to the first and second tubes to reverse the phase of the input signals before they are applied to the grid of the first tube.

A still further feature relates to the novel organization,

arrangement and relative interconnection of parts which cooperate to provide an improved amplifier of the generic cathode load or cathode follower output circuit type.

In the drawing,

Fig. 1 represents a conventional cathode load'or cathode follower electron tube amplifier.

Fig. 2a represents a typical signal input wave form, and

Fig. 217 represents the corresponding output wave form from the amplifier of Fig. 1.

Fig. 3 represents an amplifier embodying the principles of the invention.

Fig. 4a represents a typical signal wave input, and

Fig. 4b represents the corresponding wave output of the amplifier of Fig. 3.

Fig. 5 represents a modification of Fig. 3.

Referring to Fig. 1, there is shown in schematic form, a typical electron tube amplifier of the cathode follower type, comprising a grid-controlled electron tube 1, having its control grid 2 excited by the input signals applied to the input terminals 3, 4. The plate 5 of the tube is supplied with the usual high voltage direct current from any conventional plate power supply connected to the (B+) terminal 6. The electron-emitting cathode 7 is returned to the common terminal 4 through a suitable load resistor 8, and thence to the negative end of the direct current power supply connected to terminal (B). The signal output 'of the amplifier is connected across the resistor 8. Usually this output includes a circuit containing a substantial capacitance represented by condenser 9 and an equivalent shunt resistor 10. One of the advantages of this general type of amplifier is that using a high mutual conductance tube 1, the plate-tocathode impedance of this tube can be made comparatively low for positive or rising wave fronts of the input signals applied to grid 2. However, for falling or negative wave fronts, the same value of output impedance of the amplifier is not maintained. In many circuit applications, it is particularly desirable, for example in the field of television, to apply video modulating signals to a television carrier while obtaining equally fast fall and rise characteristics in the wave fronts of the modulating signals. This is particularly true where the input signals are in the form of positive and negative pulses or in the form of square or rectangular Waves having sharply rising and sharply falling wave fronts. In other applications it is often desirable to use a square wave which must be passed through or to a utilization circuit for test purposes and the like. For example, such a wave is shown in Fig. 2a of the drawing. The resultant output wave corresponding to this input wave using the conventional cathode follower amplifier of Fig. l, is illustrated in Fig. 2b. It will be observed that the curve of'Fig. 2b shows a distorted wave front 11a as compared with the corresponding wave front 11 of the input signal.

One of the reasons for this distortion is as follows. When the input signals applied to grid 2 are in the positive phase or rising direction represented by the portion 12 (Fig. 2a), the grid 2 is driven more positive, and therefore decreases the plate-to-cathode impedance of tube 1. If the tube 1 is a high mutual conductance tube, this impedance can be made quite low, and therefore the output wave front 12a can rise substantially as fast as the corresponding wave front 12 of the input circuit even though the load or utilization circuit contains substantial capacitance. It will be understood, of course, that this same effect is obtained even though the utilization circuit comprises a 'load of a complex nature including inductive, capacitive and resistive components. However, when the input signals are in the negative phase or falling characteristic represented by the wave front 11 (Fig. 2a), tube 1 can only cut off its plate current and allow the capacitance 9 in the utilization circuit to discharge through the cathode load resistance 8. It is not economical of power to make the resistor 8 as low as the plate-to-cathode impedance of the tube 1 corresponding to positive phase input signals. In fact, resistor 8 is usually chosen of the order of ten times the plate resistance of tube 1, therefore the output load capacitance 9 must be discharged through a much higher resistance when the grid 2 is excited with negative phase pulses, as

compared with its discharge resistance when the grid 2 is pulses. This accounts for the noticeable exponential decay 11a of relatively long duration in the resultant discharge Wave front.

Fig. 3 shows an amplifier arrangement wherein the advantages of the cathode load or cathode follower amplifier are obtained both for positive phase and negative phase input excitations. In this circuit, the tube 13 may be the same as tube 1, comprising the usual electronemitting cathode 14, thecontrol grid 15, and the plate or anode 16. The grid 15, instead of being driven in phase with the input signals at terminals 17 and 18, is driven in opposite phase. This phase reversal being-approximately is obtained by means of another gridcontrolled tube 19 having the electron-emitting cathode 20, the control grid 21, and the plate or anode 22. The input signals are then applied across the control grid 21 and the cathode 20 in the conventional manner. The plate 22 of tube 19 is supplied with the usual high voltage direct current potential from the (B+) terminal 23 through a suitable load resistor 24. Likewise, the plate 16 of tube 13 is also supplied with the requisite positive direct current potential from the terminal 23. The cathode return circuit of tube 13 comprises the plate-tocathode discharge path of another grid-controlled tube 25 having the usual electron-emitting cathode 26, control grid 27, and plate anode 28. The cathode 26 is returned to the common input terminal 18 which is connected to the (B-) terminal of the direct current power supply,

excited by positive phase and the grid 27 is likewise connected to the input terminal 17. The plate 28 is connected directly to the cathode 14- so that the potential for plate 28 is in phase with the potentlal variations at cathode 14. The utilization circult 29 has one terminal connected to the cathode 14 and the other terminal connected to the cathode 26.

From the arrangement shown in Fig. 3, it will be seen that the cathode load resistance for tube 13, since it is constituted of the tube 25, is variable in accordance with the input signals, and the plate-to-cathode resistance of tube 25 may be given any desired non-linear value compared with the value of the input signal applied to grids 15, 21 and 27. The net result is that when fast or steeply rising wave fronts 11 and 12 of the input signals are applied to the amplifier, the corresponding output signals have substantially identical wave fronts 11a, 12a. In other words, considering the positive or rising portions 12 of the input signal, these positive phase signals being applied in phase to the grid 27, correspondingly reduce the plate-to-cathode impedance of tube 25. Likewise, when the input signals are in negative phase, by means of the phase reversal effected by tube 19, they correspondingly reduce the plate-to-cathode resistance of tube 13 which is connected in series between the (13+) terminal 23 and the (B-) terminal through the plate-to-cathode discharge path of tube 25. Thus, the effective discharge resistance connected across the output load capacitance 30 can be arranged so as to have substantially the same value regardless of the phase of the input signals applied to grid 21.

While the drawing shows the tubes 13, 19 and 25 as triodes, it will be understood that any other grid-controlled tubes such as shield grid tubes, pentodes, beam power tubes, or the like, may be employed. Furthermore, while the tubes 19 and 25 are shown as contained within separate envelopes or bulbs, it will be understood that they may be enclosed Within a single evacuated bulb or envelope.

Fig. shows an amplifier system similar to that of Fig. 3, wherein the tube 13 is replaced by a pentode or beam power tube 31, and the tubes 19 and 25 are replaced by dual pentode or beam power tube 32. The direct current power supply potentials for the output anodes or plates 33, 34, 35, are derived from a wellregulated direct current power supply of which the (B+) terminal 36 and the corresponding (B-) terminal are shown. In the well-known manner, the beam-forming plates 37, 38, 39, 40, 41, .2, are connected directly to their respective cathodes 43, 44 and 45. The shield grids 46, 47, of the dual pentode 32, are connected together and to an appropriate positive direct current terminal 48 of the direct current power supply. The control grids 49, 50, are connected through a suitable negative bias battery or other direct current bias source 51 to the signal input terminal 52, the other signal input terminal 53 being connected directly to both cathodes 44 and 45. Preferably, the plate 34 is connected to the direct current terminal 36 through a suitable load resistor 54. The plate 34 is connected directly to the control grid 55 of tube 31, and the cathode 43 of this tube 31 is connected directly to the anode 35 of tube 32.

I have found that since the mutual conductance of the main amplifier tube 31 is of considerable importance in this type of circuit, that best results are obtained if the direct current voltage which is applied to the shield grid 56, is highly stable and well-regulated, particularly where the system is designed to operate over a very wide frequency range. If the system is designed only for short duty cycle pulse operation on the terminals 52, 53, at relatively high frequency, the conventional well by-passed power supply will suffice. If, however, the system is intended to operate over a wider frequency range extending into the low frequency response portions of the spectrum. I have found that it is highly important that the mutual conductance of tube 31 be maintained to as high a degree of stability as possible. For this purpose, there is connected across the shield grid 56 and the cathode 43, a voltage regulator tube 57 which may be of the gaseous conduction type such as the type 0B3. This tube is provided with a suitable by-pass condenser 58, so that only substantially pure and steady direct current potentials are applied to the grid 56. These potentials may be derived from a suitable high voltage direct current terminal '59 of the power supply through a series resistor 60 of suitable value. With this arrangement, the tube 3 1 extends the useful range of output voltage obtainable, since the effective mutual conductance of that tube remains substantially constant and yields a more uniform rise time at high positive output levels. If this regulation of the screen-grid voltage tube 31 is not provided, the desirable low plate-to-cathode impedance of tube 31 may not be maintained over the desired wide frequency range.

The operation of the system .of Fig. 5 is substantially similar to that of Fig. 3. The positive phase or rising wave front signals applied to grid 49 and grid 50, lower the plate impedance between plate 35 and cathode 45 which impedance is effectively across the capacitance 61 of the output or utilization circuit 62. At the same time, the phase of these signals as they reach grid 55, is shifted On the other hand, for negative or falling wave fronts, the rise in plate impedance between anode 35 and cathode 45 is compensated for by a corresponding lowering of the plate impedances of tube 31. Thus the desired low impedance in the load between the cathode follower 43 and the common return 53 is maintained for both characters of input signal.

While the invention is not limited to any particular type of electron tube, in one arrangement that was found to produce the desired results, tube 31 was a Radio Manufacturers Association type No. 807; the tube 32 was a Radio Manufacturers Association type No. 82913; and tube 57 was a Radio Manufacturers Association type No. 0133.

This particular combination of tubes was found capable of supplying sutficient output power as a modulator for a conventional signal generator. It will be understood, of course, that the particular tubes that are chosen will be determined by the amount of power that the output circuit is required to supply.

While certain specific embodiments have been described herein, various changes and modifications may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

' 1. An amplifier arrangement of the cathode follower type, comprising positive and negative D. C. supply terminals, a main amplifier tube having its anode connected to said positive terminal, another grid-controlled tube having its anode connected to the cathode of said amplifier tube, the cathode of said other tube being connected to said negative terminal, a grid-controlled phase inversion tube upon whose control grid the input signals are impressed, a substantially short circuit connection between the grid of said other tube and the grid of said phase inversion tube and means to connect the plate of said phase inversion tube to the control grid of said amplifier tube.

2. An amplifier arrangement according to claim 1, in which said amplifier tube and said other grid-controlled tube have their plate-to-cathode discharge paths connected in series across said supply terminals, and a utilization circuit is connected to the cathode of the amplifier tube to follow its potential variations.

3. An amplifier arrangement according to claim 1, in which the said amplifier tube is of the type having a control grid and a separate grid for controlling the mutual conductance of the tube, and circuit means are provided for connecting said mutual conductance control grid to a highly regulated source of direct current potential to maintain the mutual conductance of said amplifier tube constant for both positive and negative phases of input signals.

4. An amplifier arrangement according to claim 3, in which the means for applying said highly regulated potential to said separate grid includes a voltage regulator tube of the gaseous discharge type connected to a positive terminal of said direct current supply.

5. An amplifier arrangement according to claim 1, in which said amplifier tube is of the control grid and separate shield grid type and said other tube and said phase inverter tube are likewise of the control grid and separate shield grid type.

6. Amplifier apparatus for amplifying received pulses having substantially similar rectangular leading and trailing edges, comprising first, second and third grid-controlled electron tubes, means connecting the anode-cathode discharge path of the first tube in series with the anode-cathode discharge path of the second tube, an output circuit having substantial capacitance bridged across the anode-cathode discharge path of said second tube, means including .a connection between the grid of the second tube and the grid of the third tube which connection is substantially free from alternating current impedance to impress said pulses in like phase on the control grids of the second and third tubes, and circuit connections between the plate of the third tube and the control grid of the first tube for exciting the grid of the first tube by the said pulses but in phase opposition to the excitation of the grid of the third tube whereby the leading and trailing edges of the amplified pulses retain their substantially rectangular form.

7. An amplifier arrangement according to claim 1, in which said amplifier tube is of the type having a control grid and a shield grid, and a voltage regulator tube of the gaseous discharge type is bridged across the shield grid and cathode of said amplifier tube.

8. An amplifier arrangement, comprising a first gridcontrolled electron tube having a cathode load said load being constituted of the plate-to-cathode resistance of another grid-controlled tube, a utilization circuit con nected to said load to follow the variations in cathode potential of said first tube, input terminals to which input signals are applied, means including an additional electron tube between said input terminals and the control grid of said first tube and separate from said cathode load to excite the control grid of said first tube in accordance with said input signals after their phase has been shifted by approximately 180, said additional electron tube means also controlled by said signals for varying the resistance of said other tube in phase with the excitation of the control grid of said first tube, the last-mentioned means comprising a connection between the grid of said other tube and the grid of said additional tube which connection is free from frequency discrimination at high and low frequencies.

9. An amplifier arrangement, comprising a source of direct current power, first and second grid-controlled electron tubes having their plate-to-cathode discharge paths connected in series across said source, a utilization circuit connected to the cathode of the first tube to follow its potential variations, a third grid-controlled tube,

means including said third grid-controlled tube to excite the grids of the first and second tubes in phase opposition under control of the input signals, the last mentioned means including a substantially impedance-free connection between the grids of the second and third tubes.

10. An amplifier arrangement according to claim 9, in which the grid of the second tube and the grid of the third tube are connected together by a direct current connection of negligible alternating current impedance.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Text-Valley and Wallman-Vacuum Tube Amplifiers, page 438, Fig. 11.206 (curve C) and discussion thereofMcGraw Hill Pub. 1948. 

